On the theory of superexchange interaction

Abstract

The superexchange interaction for the spin coupling in certain magnetic compounds is treated on the basis of an approach which takes into account the deformation of the electron orbitals of the intervening ions. Quantitative calculations are carried out for three centre and four electron system. The polarization of the intervening ion is considered by assuming slightly different orbitals for the two electrons with anti-parallel spins. This corresponds to the procedure of taking certain excited configurations into considerations. The effect of the excited states in which one of the anion electrons changes its spin is also considered by using the perturbation method. If one regards the triplet and singlet states of the system as the representatives of the ferromagnetic and antiferromagnetic states respectively, their energy difference arises as a result of the latter effect, while the same occurs by merely considering the former deformation if one uses the single determinant approximation. A rough numerical estimate gives reasonable agreement with the observed Neel temperature for MnO.